1. Field of the Invention
This invention relates to a photosensitive composition useful as a resist composition employed in a step of fine working in the process of manufacturing a semiconductor device. In particular, this invention relates to a transparent photosensitive composition especially suited for use in a process where a short wavelength beam of not more than 160 nm in wavelength, such as a fluorine laser beam, electron beam, EUV and X rays, is employed.
2. Description of the Related Art
In the manufacturing process of electronic components including a semiconductor element, it is required to form a fine pattern by a photolithographic technique. This technique necessitates the employment of a resist and can be performed according to the following process. Namely, first of all, a resist composition is coated on the surface of substrate to form a thin film constituting a photoresist film. Then, this photoresist film is subjected to exposure, which is followed by treatments including the development and rinsing thereof to form a resist pattern. Thereafter, by using this resist pattern as an etching resistance mask, an exposed surface of the substrate is selectively etched away so as to form fine lines or openings, thus form a desired pattern. Finally, the resist pattern left remained on the substrate is removed by ashing, thus obtaining a patterned substrate.
As for the exposure apparatus employed on the occasion of forming a pattern by using a resist, there is generally employed a reducing projection type exposure apparatus or so-called stepper. According to this exposure apparatus, since the work of exposure is performed through the projection of an optical image, the resolution is limited by the wavelength of the beam employed. Along with rapid progress in multi-functionalization and densification of electronic components in recent years, there is an increasing demand for enhancing the fineness of circuits. In order to meet this demand, efforts are being made to employ a light source of shorter wavelength in the exposure, thereby making it possible to perform a finer working on the circuit. It would be imperative to employ, in the manufacture of electronic devices in the coming era of gigabit memories an F2 excimer laser having a wavelength of 157 nm as a main light source. Therefore, it is now desired to develop a resist material excellent in transparency and capable of forming a fine pattern by using an F2 excimer laser as an exposure light source.
Incidentally, a dry etching process using plasma can now be employed for finely working a substrate. Therefore, with a view to more effectively performing such a fine working as mentioned above, it is now desired to form a resist pattern by using a resist excellent in dry etching resistance.
A resist comprising an alicyclic compound, which can be employed in place of aromatic compounds has recently attracted attention. For example, Jpn. Pat. Appln. KOKAI Publication No. 4-39665 describes an alkali-developing resist excellent in dry etching resistance and in transparency to a beam of short wavelength. In this publication, there is employed a polymer which is formed of a compound comprising adamantine (or a bridged alicyclic compound) which is copolymerized with another acrylic ester-based compound so as to provide a polymer with alkali-solubility.
Further, there have been developed various resist materials, such as a resist material having a tricyclodecanyl structure as shown in Jpn. Pat. Appln. KOKAI Publication No. 7-199467 as an alicyclic compound having a five-membered ring among bridged alicyclic compounds, a resist material containing an alicyclic group-containing acrylic ester-based resin as a base material, and a resist material containing an anhydrous maleic acid-based resin as a base material. However, these materials are highly capable of absorbing the aforementioned short wavelength beam having a wavelength of 160 nm or less. Therefore, when this short wavelength beam having a wavelength of 160 nm or less is employed as an exposure light source for the etching of a resist film comprising any of these resist materials, it is impossible to enable the exposure beam of such a short wavelength to reach a sufficient depth from the surface of the resist film. Accordingly, there is a problem that it is difficult, even if these conventional resist materials are employed, to obtain a desired fine pattern by using a short wavelength beam having a wavelength of 160 nm or less as an exposure light source.